1. Field of the Invention
The invention relates to a vehicle wheel state monitoring device and method, and more particularly to a technology that monitors whether it is probable that a vehicle wheel is damaged during running of a vehicle.
2. Description of the Related Art
In order to run a vehicle safely it is essential to maintain the vehicle wheels, which include both tires and wheels, in a normal state. Accordingly, if an abnormality of the vehicle wheels occurs, such as when the air pressure of the tires is inadequate or the tires or wheels are damaged, it is important to rapidly detect the abnormality and inform the driver and/or passengers so that appropriate measures can be taken. Various technologies have been disclosed that detect the occurrence of abnormalities of vehicle wheels by monitoring the state of the vehicle wheels.
A vehicle is not always fitted with the same type of vehicle wheel, and thus it is necessary to change a detection method used for detecting the occurrence of abnormalities depending on the type of vehicle wheel being used. For example, Japanese Patent Publication No. JP 2000-318416 A discloses a technology that distinguishes a type of vehicle wheel based on a relationship between a tire air pressure and a spring constant of a spring under the vehicle body, and then detects a vehicle running characteristic for each specified type of vehicle wheel. Moreover, Japanese Patent Publication No. JP 2004-98877 A discloses a tire air pressure reduction warning method in which a threshold value is used for determining whether an internal pressure of a tire has reduced. The threshold value is set in accordance with the type of vehicle wheel fitted to the vehicle.
However, the above described technologies do not disclose any method for handling a situation when different types of run-flat tire wheels are fitted to the vehicle, such as run-flat tire wheels with reinforced sides or with an inner support ring. Accordingly, in such situations, accurate abnormality detection may be impossible.